Oxidation of hydrocarbons to borate esters



March 29, 1966 c. N. wlNNlcK OXIDATION OF HYDROCARBONS TO BORATE ESTERSFiled July 26. 1965 INVENTOR.

CHA/HES lV. W/NN/CK ATTORNEE United States Patent O 3,243,449 OXIDATIGNOF HYDRGCARBONS T BORATE ESTERS Charles N. Winnck, Teaneck, NJ.,assignor to Halton International, Inc., a corporation of Delaware Filed`luly 26, 1965, Ser. No. 474,921 12 Claims. (Cl. 2610-462) Thisapplication is a continuation-in-part of copending application SerialNo. 162,247, led December 26, 1961, now abandoned, and Serial No.202,687, filed lune 15, 1962.

The present invention is concerned with the oxidation of saturated C.,to C8 hydrocarbons with molecular oxygen in the presence of metaboricacid or a less hydrated form of ortho boric acid including boricanhydride at conditions whereby very high oxidation selectivities andeconomies are achieved.

It is broadly well-known to selectively oxidize hydrocarbons such ascyclohexane to form products including cyclohexanol and cyclohexanone.In processes for the production of adipic acid, phenol, cyclohexanone,and other important chemicals, a major step in the process involves theselective oxidation of cyclohexane. A disadvantage of prior processeshas been the generally low selectivity of the oxidation reaction. A

It is generally old and well-known that the selectivity of molecularoxygen oxidations of hydrocarbons toa corresponding alcohol can besubstantially improved by carrying out the oxidation in the presence ofboric acid or a boric acid anhydride.

Luther et al., for example, in United States Patent 1,931,501 disclosethat enhance-d alcohol production results from the molecular oxygenoxidation of hydrocarbons, including paraiins and naphthenes, boilingabove 180 C. by adding to the hydrocarbons at least 2% by weight of aweak inorganic acid such as boric acid or its anhydride. l

Hellthaler et al. in United States Patent 1,947,989 disclose oxidizinghydrocarbons with molecular oxygen in the presence of boric acid wherebyimproved oxidation selectivity to alcohol is attained.l Preferredtemperatures of 160 to 200 C. for the oxidation are taught. The processis described as capable of application in allcases where hydrocarbonscan be oxidized in the absence of boric acid.

Russian work by Bashkirov et al., Dokladay Aked. Nauk. SSr. 118, No. l,pages 149 to 152 (1958), has shown that paratiins such as tridecane canbe oxidized with nitrogen-oxygen mixtures containing 3.0-3.5 oxygen at165 l70 C. with 5% added boric acid. Highk oxidation selectivities toalcohols and ketones is shown. A paper on the Russian work wassummarized on June 3, 1959, by W. G. Toland at the Fifth World PetroleumCongress. See paper 15, section IV, Proceeding of the Fifth WorldPetroleum Congress.

In addition to boric acid and anhydrides, Aother boron compounds havebeen employed. For example, French Patent 1,166,679 teaches the use ofborate esters such as tributyl borate in hydrocarbon oxidations.

Although the oxidation of higher hydrocarbons, both paraflins andnaphthenes, with molecular oxygen in the presence of a boron `compoundas above shown is indicated as proceeding readily with the production ofalcohols in high selectivity, severe difliculties are encountered whenit is attempted to apply this technology to lighter hydrocarbons such ashexane and cyclohexane. It is, of course, obvious to attempt to applythis prior ICC technology to-C4 to C saturated hydrocarbon oxidations.

And, as expected, the oxidation selectivity can in some instances besomewhat improved when following the prior art teachings.

However, it has not heretofore been possible with the volatile C4 to C8hydrocarbons to provide a molecular oxygen oxidation process havingreaction selectivities coinparable to those achieved with the heavierhydrocarbons while at the same time having favorable economies ofoperation.

For example, the Russian workers above described assert that in order toachieve high reaction selectivity it is necessary to operate with verylow oxygen pressure, and in oxidation systems involving higherhydrocarbons the oxidant oxygen partial pressure can be lowered with butsmall reaction system changes. However, in the oxidation of the C4 to CBhydrocarbons the oxygen partial pressure caniiot be similarly loweredwithout rendering the process uneconomical and impractical. Heat inputrequirements necessary to maintain reaction conditions become excessivewith the higher hydrocarbon sys- Further, although prior workers haverecognized that water removal is an important consideration in theoxidation of hydrocarbons such as hexane, problems associated with waterremoval have prevented successful application of the heavier hydrocarbonboric acid oxidation technology to lighter, more Volatile hydrocarbonssuch as' hexane.

For example, in the discussion following the presentation of the Russianpaper by W.- G. Toland, above referred to, at the Fifth World PetroleumCongress, H. M.4

- susceptible to oxidation.

If one tries to apply this process, this technique, to the lower andmore volatile parains, this limitation becomes immediately apparent, andin fact in our laboratories,

is provided a novel and improved method for the molecu-y lar oxygenoxidation of saturated hydrocarbons having 4 to 8 carbon atoms.

The oxidation ofthis invention is carried out in a batchwise orcontinuous manner by contacting gaseous molecular oxygen with a mixtureof liquid hydrocarbon and meta boric acid or a less hydrated derivativeat a contact temperature in the range of about to 180 C. As an essentialof the present invention, the reaction is so maintained that the partialpressure of water in the exit gases, i.e., the vapor above the liquidreaction mixture, in p.s.i. a., is not greater than P where P is givenby the expression:

(1) logn, P=0.0iii2T-0.2759 and most desirably not greater than P whereP is given by: (2) log, P=0.0175T 1.85

where T is the reaction temperature in degrees C.

FIGURE 1 is a graph illustrating reaction selectivity versus conversion.It also demonstrates the effect of water partial pressure on theselectivity conversion relationship. This graph represents a statisticalaveraging of several Patented Mar. 29, 1966 hundred oxidations by meansof a regression analysis. Statistical analyses have shown the curves toaccurately predict true -selectivities to within 1 point. Consequently,it is far more meaningful for allowing a finely accurate prediction ofperformance kthan any one or two runs where one can encounter deviationsfrom the statistical mean values greater than 1 point.

Desirably, the Voxidation of this invention is carried out in abatchwise or continuous manner by contacting gaseous molecular oxygenwith a mixture of liquid hydrocarbon and meta-boric acid at a reactiontemperature in the range of 140 to 180 C. During the ,reaction a gaseousmixture comprising water and hydrocarbon, and usually also containinginert gas such as nitrogen, is removed from the reaction zone. In thispracticerof the present inventive process the reaction is so maintainedthat the partial pressure of water in this exiting gas mixture inp.s.i.a. is not greater than P as given in Equation 1 above, preferablynotrgreater than about 70% of P as given in Equation 1, desirably notgreater than P as given in Equation 2, and most desirably 2 to 100% of Pas given in Equation 2. y

Through practice of the present invention, hydrocarbon oxidationreactionselectivities in excess of 80 to 85% to products from whichcorresponding alcohols and ketones are readily recovered can be attainedwith high economies of operation.

Hydrocarbons which are oxidized by the process of this invention includecyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclohexane, the dimethyl cyclohexanes, n`pentene, n-hexane, n-heptane,the methyl pentanes, and the like. In preferred operation, and admixtureof the hydrocarbon together with a selectivity Vpromoting amount ofmeta-boric acid or lower boric acid hydrate is formed. In a desirableembodiment of the invention, a slurry of ortho boric acid in thehydrocarbon is rst formed. This slurry issubjected to a dehydrationtreatment as by passing a gas therethrough at elevated temperature todehydrate at least part and lpreferably substantially all of the orthoboric acid'. Other methods for v problems of slurry Vhandling inthereaction and solids separation difficulties, it is generally notdesirable t-o employ amounts of the boron compound expressed asmetaboric acid in excess of about 20% by weight of the Ihydr0-`rcarbon-boron compound admixture. y

Meta-boric acid is preferably employed in this invention. Included amongthe lower hydrates of boric acid which also can be used are boron oxideand tetra-boric acid. By lower hydrates is meant derivatives of orthoboric .acid formed by removal of water. When 1lower hydrates areemployed, and the partial pressure of water in the, vapors over thereaction mixture is above the equioxygen can be used, it is preferred touse molecular oxygen in admixture with inert gas such as nitrogen.Concentrations of oxygen, greater or lesser than those found in airequaling 4 to 25%, can be used. It is generally preferred to employoxygen concentrations by volume of 10% or less in the oxidant gastoavoid possible formation of explosive mixture.

During the oxidation reaction, a gaseous mixture comprising such inertgas as is in the feed oxidant stream together with any unconsumed oxygenand water and hydrocarbon vapor is continuously removed from thereaction zone. The hydrocarbon vapor may be condensed, at leastpartially separated from water, and returned to the reactor as a liquid.Normally, lthe amount of water in the reaction zone and theconcentration of this water in the gases exiting from the reaction zoneis substantially dependent upon the oxygen concentration'in the oxidantgas stream and consumption during the reaction. However, additionalpossible sources of Water include the feed gases, the feed hydrocarbonmixture, and reux hydrocarbons from which a portion of the water hasgenerally been removed by decantation, stripping or the like.

When meta-boric acid is used, the oxidation reaction is so conductedthat the water partialv pressure in the vapor stream leaving the liquidreaction mixture in p.s.i.a. is 0.3% to 100% of P in accordance with theexpression with T being the reaction temperature in degrees C., andpreferably 0.3% to 70%. Y

When lower boric acid hydrates such as boron oxide are employed, pureoxygen and cooling can be employed inthe reaction. It is possible to usesuicient amounts of the lower hydrate such that these hydrates reactwith water which is formed during the reaction or which is introducedinto the reaction mixtu-re with feed materials such that the partialpressure of waterin the vapor above the reaction mixture is not greaterthan P as above described without the necessity of vapor removal fromthe reaction zone.V Of course, gradations of operation are possible suchthat the process can be operated adiabatically or with heat 'input usingthese lower hydrates.y Whereas, using meta-boric acid, as abovedescribed it is essential thatthe Water partial Vpressure in the exitvapors be at least 0.3% of P, with the lower hydrates forv economicoperation it is necessary only thatV the water partial pressure inthevapor above the reaction mixl ture be no greater than P.

In practice ofv this invention wherein the hydrocarbons which areoxidized ,are C4 to C7 hydrocarbons, and the oxidation is carried out inthe absence of solvent and of' large amounts of lowerY hydrates, theprocess often Y within the range above designated while operating at thelibrium pressure, the lower hydrates will tend to be conf verted tohigher hydrates and even to meta-boric acid. It is a feature of thepresent invention that generally higher hydrocarbon conversions per passcan be achieved without the selectivity decrease which accompanied suchhigher conversions in prior yoxidation processes. The oxidation of thisinvention iscarriedlout such that about 4 to 25% desirably 8 to 20%, andpreferably l0gto 15% of the hydrocarbon is oxidizedper pass in acontinuous system `or per oxidation in a batch operation.

Suitably, the admixture of boron compound, preferably meta-boric acid,and hydrocarbon is heated to the 140 to 180 C.V oxidation temperatureand a vgas containing molecular oxygeny is passed therethrough. AlthoughVpureV desired reaction temperature. The heat input Ycan be accomplishedin a variety of ways. Preferably, hydrocarbon removal from the reactionzone as vapor upon condensation `and separation from water is heatedand/ or is vaporized and introduced into the reaction zone as vapor.Alternatively, heat can be provided through the reactorY walls, byvmeans of heating coils in theY reaction zone, and the like.v

With C8 hydrocarbons, it is more often possible to op-` erateadi'abatically, in .accordance with the invention. That is, the. heatliberated by the reaction is about suicient to provide the heatnecessary for water and hydrof carbon vaporization.

It is possible to carry out the invention such .that a solvent isemployed in the reaction mixture.' Suitable solvents areV those Vwhichare inert during the oxidation and which can be readily separated fromthe reactants and reaction products. Desirably organic compounds havingnoy reactive secondary or tertiary carbon atoms are employed. Hydrogenson primary carbon atoms are substantially inert in the present reaction.However, hydrogens on secondary and tertiary carbon atoms tend to bemuch more reactive in this reaction.

Preferably the compounds boil intermediate the hydrocarbon to beoxidized and the lowest boiling of the oxidation products. Illustrativesolvents include hexamethyl ethane, neopentane, ethyl acetate,ditertiary butyl ether, substituted benzenes, halogenated hydrocarbonsand the like.

It is to be noted that the presence of a solvent will change thecharacteristics of the reaction system. Thus, where the solvent ishigher boiling than the hydrocarbon, the reaction will be able to becarried out under more nearly adiabatic conditions and in fact coolingmay be required even for the C4 to C7 hydrocarbons.

Successful practice of this invention requires careful control andregulation of the reaction conditions. Thus, the oxidation reactiontemperature must be in the range 140 to 180 C. and preferably 160 to 170C. In actual practice in an experimental unit an exact reactiontemperature is selected; a reaction pressure is then calculated onconsideration of the hydrocarbon system in the reaction (with or Withoutsolvent), the quantity of inerts fed to the reactor, and the quantity ofwater required to be removed, such that the volume of organics, inerts,and oxygen which may not be consumed leaving the reactor as vapor issuflicient to maintain the water pressure within the limits cited above;the heat transfer to the reactor is then adjusted so that the desiredtemperature and pressure conditions are met. In an alternate method ofoperation, the same calculation would be made, but the heat transfercould be adjusted to maintain the desired flow of organic vaporsoverhead, while the pressure would be adjusted to control reactortemperature. Illustrative pressures are in the range to 800 p.s.i.g.

For example, in the case of the oxidation of cyclohexane using asoxidizing gas air diluted with nitrogen to a volumeric concentration ofoxygen of 10%, a reaction temperature of 165 C. is preferred. At thistemperature, the vapor pressure of the liquid cyclohexane is about 105p.s.i.a.

It is desirable and important to -operate at conditions of substantiallycomplete oxygen consumption in order to make the most eicient use of thecompressed oxidizing gas and to avoid explosion hazards. In the highlyselective reaction of the present process, between about 1.0 and about1.5 moles of water are formed per mol of oxygen consumed with verylittle carbon dioxide forma tion. Water contained in the feeds to theoxidation zone must likewise be removed in the manner of control of thisinvention. However, it is suitably illustrative to demonstrate thetechnique for the ideal case where there is no water in the feeds. Thus,using 10% oxygen as oxidizing gas, the water plus inerts in theoxidizing zone will be about 90 moles N2 and 10 to 15 moles of water per100 moles of inlet oxidizing gas.

With the above parameters, in order to control the Water partialpressure in the exit gas at low level of the order of 2 p.s.i.a. thesystem pressure is determined by the sum of the vapor pressure ofcyclohexane plus the pressure exerted by the water vapor plus inerts,For a Water partial pressure of 2 p.s.i.a. for 90 percent N?, and 10percent water, the sum of N2 plus water partial pressures would bep.s.i.a. The system pressure then would be 20 p.s.i.a. plus the 105p.s.i.a. cyclohexane vapor pressure, or 125 p.s.i.a. Similarly, for 85,5percent nitrogen and 14.5 percent Water (90 moles NZ-lS moles Water) fora 2 p.s.i.a. water partial pressure the system pressure is 14 -plus 105or 119 p.s.i.a.

Thus, the reaction system would be operated at a pressure -in the rangeof 119-125 p.s.i.a. with provision of sucent heat to maintain reactiontemperature and pressure. A precise control to 2 p.s.i.a. water pressureis attained by analysis of the reactor ot gases for water andappropriate pressure regulation.

In an alternate method of operation, the same calculation would be made,but the heat transfer could be adjusted to maintain the desired flow oforganic vapors overhead, while the pressure would be adjusted to controlreactor temperature. Illustrative pressures are in the range 10 to 800p.s.i.g.

In desirable economic operation of the invention, the vapor mixture fromthe reaction zone is cooled to con-l dense water and hydrocarbon. Thesecondensed materials are separated as by decantation and the hydrocarbonreturned to the reaction zone. Heat economies are achieved by heatexchange between the hydrocarbon returning to the reaction zone andvapors exiting from the reaction zone; if direct contact is used forsuch heat exchange, further stripping of water from the returninghydrocar bon is also accomplished. Heat necessary to sustain thereaction is preferably provided by heating the recycle hydrocarbon priorto introduction into the reaction zone.

At the termination of the oxidation reaction, the 4reaction mixturecontains a substantial amount of the alkanol in the form of a borateester thereof. If desired the borate ester can be recovered as such. Inorder to recover the alkanol as such it is desirable to subject theoxidation reaction mixture after removal of unreacted hydrocarbon to ahydrolysis whereby the alkanol liberated can readily be recovered bydistillation, for example, by adding water to the oxidation reactionmixture after hydrocarbon removal and heating, e.g. to 50-150 C. Otherknown type techniques such as alcoholysis, transesteritication, and thelike can be employed.

Accompanying FIG. 1 demonstrates the importance of water partialpressure on oxidation selectivity over a wide conversion range. The dataillustrated in FIGURE 1 were obtained by analysis of a great number ofcyclohexane oxidation runs using added meta-boric acid with widevariations in operating conditions. The critical effect of water partialpressure on the reaction selectivity is apparent from the gure. Forexample, referring to the figure, at conditions of constant conversionit is seen that reaction selectivity sharply decreases as the waterypartial pressure increases. At 10% conversion, for example, at 3p.s.i.a. water partial pressure selectivity to cyclohexanol pluscyclohexanone is about 88% whereas at 16.8 p.s.i.a. the selectivity isabout 81% For comparison purposes, also presented in FIGURE l is a curveshowing selectivity versus conversion for cyclohexane oxidationsnotinvolving the use of boron adjuvant. The single curve is valid over awide range of water partial pressures since water partial pressure isnot an important factor effecting reaction selectivity in sys-v temswhich do not employ the meta-boric acid or less hydrated ortho boricacid form.

In systems not employing meta-boric acid or the like, water does notsignificantly influence the rea-ction selectivity. Water does tend toinhibit the oxidation itself, and tne presence of high amounts of waterhas in thel prior art necessitated higher temperatures to overcome theinhibiting effect. However, the actual selectivity of the re'- action isVirtually independent of water partial pressure.

In the following examples, unless otherwise specified parts andpercentages are given by weight.

EXAMPLE I Cyclohexane in amount of 2711 parts is mixed with about 450parts of iinely ground solid ortho-boric acid. The resulting slurry isheated to about 165 in an agitated, baied, glass-lined reactor equippedwith heating jacket, vapor take-off, condenser, vapor-liquid separator,water separator and reflux return line, and a nitrogen stream passedtherethrough at p.s.i.g. The ortho-boric acid readily dehydratessubstantially completely to meta-boric acid, and a gaseous mixture ofnitrogen, Water vapor and The resulting -slurry of meta-boric acid incyclo hexane is maintained at 165 C. by adjusting the heat supply to thejacket as required. A gaseous mixture Ofv 4% by Volume oxygen innitrogen is introduced into the reactor'below the liquid surface` at arate of about 4 volumes per minute `(1 atm. and 25 C.) per about 3.8volumes of slurry. Oxygen absorption is substantially complete after ashort .period of time. The pressure in the reaction zone is maintainedat 120 p.s.i.g. (134-.7 p.s.i.a.) by means of a pressure rcontrol valveon the vapors leaving the vapor-liquid separator. At these reactionconditions, t'he oxygen partial pressure vat the point of entry into thereaction zone is about 1.2 p.s.i.a. taking into consideration the.cyclohexane vapor pressure of 105 p.s.i.a.

at thereaction temperature (i.e.: 4% of 134.7-105).

During the reaction a vapor mixture comprising cyclohexane, Water andnitrogen is continuously removed from the reaction zone and cooledtocondense water and cyclohexane. Vapors are separated from condensate finthe separator. After separation from Water by decantation the liquidcyclohexane is recycled to the reactor. Under the above reactionconditions, the water partial pressure in the gases exiting from thereaction zone is about 1.6 p.s.i.a.

After completion of the reaction (about 6 hours), the reaction mixtureis admixed with 200 partsof Water and agitated under reflux ofwater-hydrocarbon azeotrope (about 70 C.) for 1 hour to .hydrolyzeborate esters.

The resulting mixture is filtered to separate solid ortho-p boric acidand the ltrate is decanted to separate an organic phase from an aqueousphase. The aqueous phase is extracted With a small amount of cyclohexane4and the extract is combined with theorganic phase; The organic phase isextracted with a small Aamount ot water to remove ortho-boric acid. .Theresulting extracted organic mixture is distilled to separate cyclohexaneoverhead from a bottoms cyclohexanol fraction. The cyclohexanol fractionin the amount of 360 parts ycontains about 82% cyclo- Vhexanol and 3%cyclohexanone, andv the remainder other oxygenated cyclohexane products.

The cyclohexane conversion is about 11% EXAMPLE II In anothercomparative example, the importance vof maintaining the temperaturewithin the speciiied 140C. to 180 C. range is illustrated.

Example I is repeated except that a slurry of 100 parts of othro-boricacid in 1000 parts of cyclohexane is dehydrated and the resultingmixture of meta boric acid and cyclohexane is oxidized for 4- hours at200 C. and 253 p.s.i.a; Oxidant gas comprising by volume 4% oxygen inVEXAMPLE III As further comparison, illustrating operation which iS notwithin the scope of the present inventive process, a slurry of 900 partsof cycl-ohexane and 231 parts of boron oxide is formed. About 100 p.p.m.of cobalt based on cyclohexane` is added as cobalt naphthenate.

Air is passed through this slurry at a rate of about v170 volumes perhour per 1.3 volumes of slurry. The

reaction is carried out at a temperature of' 190 C. and at a pressure of200 p.s.i.g. Oxygen absorptionafter minutes reaction time is about 32volumes.

The reaction mixture is Worked up as described in Example -I. About 12%of the cyclohexane is converted Within reaction selectivity tocyclohexanol of 67.6% and a selectivity to cyclohexan'one of 3.9%

The total selectivity to cyclohexanol and cyclohexanone of 71.5%illustrates that` by the process of this example little or noselectivity improvement is achieved 4as con-` trasted with cyclohexaneoperation not employing a boron compound.

EXAMPLE IV As a further comparison, it is attempted `to carry out theoxidation as described in Example I at a temperature of C. No reactionisobtained. This example illustrates the importance .of the'lowerspecied temperature of the present invention. f

EXAMPLE Vl An admixture of 66 parts of iinely ground ortho-boric acid in660 parts vof n-hexane is dehydrated and oxidized as described in`Example I. The reaction temperature is C., and reaction pressure 170p.s.i.g. Oxidant gas consistent of 4% oxygen in nitrogen is 'employed ata rate of about 137 volumes Vper hour per volume of slurry. Inlet oxygenpartial pressure is about 1.7 p.s.i.a. and exit gas Water partialpressure lis about 2.2 p.s.i.a. Oxidation is 4 hours, heat input bymeans of vaporized recycle hexane is maintained suicient to provide forwater removal at the rate at which it is formed in and introduced intothe vreaction zone.

After working up as in Example I, at 7% hexane convver-sion theselectivity to alcohol plus ketone is 86%.

EXAMPLE VI An admixture comprising a slurry of 10.0 parts of meta boricacidin 1000parts vof methyl cyclohexane is oxidized in a manner similarto that .described inlExarnple I. The reaction temperature is 160 C. andthe reaction pressure is 62 p.s.i.g. Oxidant gas consisting of 8% oxygenin nitrogen is employed at a rate ot about v volumes per hour per 1.3volumes of slurry.Y Then Ioxidation is continued until Y24 liters ofoxygen is absorbed.

The inletoxygen .partial pressure is about 1 .34 p.s.i.a. and the .exitgaswater partial pressure is. about 1.74-p.s.i.a. Heat input by means ofVvaporized .recycle methyl ,cyclohexane is maintained sufficient toprovide for` water re- `moval at Athe rate at which it is formed in andintroduced vinto the reaction zone. About 10% of the methyl cyclohexaneis reacted. A

After working upV as in Example I, the overall selectivity1to alcohol`plus ketone is about 78%. 1-methyl cyclohexanol is formed in amount ofabout 26%, 2- methyl cyclohexanol is formed in amount of about 17 3-and4-rnethyl cyclohexanols together are formed in amount of about 28%,and a mixture of methyl cyclohexanones in amount of about 6% is formed.

Y EXAMPLE VII Example V is repeated substituting n-heptane in'place .ofthe methyl cyclohexane. Generally similar selectivity to alcohol plusketone Aare obtained. K l

EXAMPLE vm A glass line reactor equipped with a vapor take-olf,condenser and water separator was used. During the reaction, vapors werecontinuously removed, condensed, Water separated and the cyclohexanereturned to the reaction.

At the termination of the reaction, the resulting mixture was distilledto separate unreacted cyclohexane, and the thusly obtained oxidationreaction mixture was hydrolyzed. The hydrolysis was accomplished byadding Water and heating to about 80-1'00" C. Thecyclohexanol-cyclohexanone product was recovered by decantation andsteam distillation.

The following table shows the results obtained. Run D wherein no 'boroncompound was used is included for purpose of comparison.

EXAMPLE X111 Example I is repeated except that a gaseous mixture of 10%by volume oxygen in nitrogen is employed. The

Table I Run A B C D E oyciohexsne, parts 2,711 2, 684 2,740 2, 000 2,750Boron compound, parts- 303 154 84 None 456 Cyelohexanone, parts 5 5 5None None Airow rate, l./min 2.4 2 2.4 4.4 12.4 Reaction Temperature,0.--. 173-170 163-164 168-174 157-158 165-167 Reaction pressure, p.s.i.g120 125 150 120 O2 Uptake (approx.) liters 54 51 74 50 Cyclohexanereacted, percent 7. 6 7.8 6. 7 8. 3 14. 4 Reaction selectivity toeyclohexan and eyclohexanone, percent 80 76 80 61 90 Ratiocyelohexanol/eyclohexanone 19. 3/1 4.7/1 3.9/1 l 1.2/1 31/1 Waterpartial pressure in eiuent gas,

psig 2.5-4.2 V8.5-9.0 S14-12.7 17. 80-1a0 1.1-1.3

1 4% oxygen in nitrogen. The above results show the improved oxidationselectivity reaction Zone pressure is maintained at about 259 p.s.i.a.to cycloalkanol and cycloalkanone obtained through the At the reactionconditions, the oxygen partial pressure use of the specified boroncompounds. The results also at the point of entry into the reaction zoneis about 15.4 establish the very high selectivity to cycloallcanolattained psig, taking into consideration the cyclohexane vapor throughthe use of the higher amounts of boron Compressure of 105 p.s.i.a. atthe165 C. reaction temperature pounds. For example, in Runs A and Eselectvities (eg, 10% of 259-105). Vapors are removed as detOCYCOheXaHOl and CYCIOheXaHODe Were Obtained Which scribed` in Example I.Under these reaction conditions, were about 130 to 150% that `ObtainedWhere 110 bOrOIl thewater partial pressure in the gases exiting from theCompound Was employed (RUB D) M3111/ fold improve' reaction zone isabout 20 p.s.i.a. ments in SeleCtVtY t0 CYCOheXaDOl Were attained as Thereaction `is continued until about 10.5% of the shown in the above data.cyclohexane is reacted. The reaction mixture is Worked EXAMPLE 1X up asdescribed in Example I. AMolar selectivity to cyclohexanol pluscyclohexanone is found to be 80%, with a Runs A, B, C and E 0f ExampleVIH were repeFted ratio of cyclohexanol to cyclohexanone of about 6:1.using cyclooctane instead of cyclohexane. Substantially EXAMPLE XIVsimilar percentage improvements in reaction selectivity to cyclooctanoland cyclooctanone and in the cycloocta- Example 1S repeated etCePt thata faSeOUS mlXtUfe 0f nol to cyclooctanone ratio were obtained ascontrasted 10%.135 Volume OXYgeIl 1n .Dltff'gefl 1S employed The withoperation employing no boron compund reaction zone pressure 1s maintamedat about 336 p.s.1.a. At the reaction conditions, the oxygen partialpressure at EXAMPLE X the point of entry into the reaction zone is about23 p.s.i.a. Runs A, B, C and E of Example VIII were repeated taking intoconsideration the cyclohexane vapor pressure using cyclopentane insteadof cyclohexane. Substantially 0f 105 p.s.i.a. at the 165 C. reactiontemperature (i.e., similar percentage improvements in reactionselectivity 10% of 336-105). Vapors are removed as described in tocyclopentanol and cyclopentanone and in the cyclo- Example I. Underthese reaction conditions, the water pentanol to cyclopentanone ratiowere obtained as conpartial pressure in the gases exiting from thereaction trasted with operation employing no boron compound. zorrieh isabout 30 p.s.i.a. d 1 b 7 f e reaction is continue unti a out 9.0 o othe cyclo- EXAMPLE XI hexane is reacted. The reaction mixture is Workedup as Runs A, B, C and E of Example VIII were repeated described inExample I. Molar selectivity to cyclohexanol using cycloheptane insteadof cyclohexane. Substantially plus cyclohexanone is found to -be 80%.similar percentage improvements in reaction selectivity to The presentinventive process can be carried out withcycloheptanol andcycloheptanone and in the cyclohepout a catalyst. In previous processeswhich did not emtanol to cycloheptanone ratio were obtained ascontrasted ploy a boron compound, it was necessary to employ small withoperation employing no boron compound. amounts of a catalytic materialsuch as cobalt salt in order EXAMPLE XH to successfully oxidizecyclohexane with molecular oxygen to a mixture which comprisedcyclohexanone and cyclo- Methylcyclohexane was oxidized 1n accordancewith the 70 heXanOL However, in the present process whereinmolecinvention in a manner similar to that described in Ex- 'ulmoxygenis contaeted with the mixture of metab0ri ample VIII, Run E. Thefollowing table shows reaction Iacid and hydrocarbons under the statedconditions, it has conditions and the results obtained. A run withoutthe vbeen found that materials previously used as catalysts in use ofboron compound is presented for purposes of comnon-boric acid oxidationshave substantially no effect or parison. l I- possibly an adverse eifectand thus are not required.

11 Initiators such as aldehydesfketones, and peroxides can Vbe used.Illustrative of such initiator is cyclohexanone, hydrogen peroxide,tertiary butyl hydroperoxide, and the like. t

EXAMPLE XV Cyclohexane is continuously oxidizedin a series of fourreactors at a temperature ofu165 C. and a pressure of 140 p.s.i.a. usingas oxidizing gas 10 vol. percent O2 and 90 vol. percent N2.

To the -rst reactor is added per hour 2750 mols of liquid commercialpurity cyclohexane and ,.67 rn,ols metaboric acid preheated to Vabout165 C. Also introduced into the first reactor per hour are 440 mols ofcyclohexane vapor at about 165 C. and 240 moles of said oxidizing gas.

A vapor mixture of about 770 moles cyclohexane, 207 moles N2, 2 molesunreacted O2, and about 25 moles water per hour is removed from theiirst reactor.

A liquid stream containingabout 2395 moles cyclohexane and about molesoxidized cyclohexane'iscon-Y tinuously passed from the rst to thesecond' reactor. About 350 moles cyclohexane vapor at about 165 C. and210 moles of oxidizing gas were introduced into the second reactor.

A vapor mixture of about 680 moles cyclohexane, 18 moles nitrogen and 25moles water was removed per hour from the second reactor. A liquidmixture containing about 2040 moles cyclohexane and 50 moles oxidizedcyclohexane was transferred per hour from the second to the thirdreactor. f

About 330 mol cyclohexane vapor at about 165 C. and 210 moles oxidizinggas were introduced per hour into said third reactor and contacted withthe liquid mixture.

From the third reactor there was withdrawn per hour a vapor mixture ofabout660 moles cyclohexane, 189 moles nitrogen and 25'mol`es water andalso a liquid mixture containing about 1685 moles cyclohexane 'and 75moles oxidized cyclohexane which was sent to the fourth reactor.

About 290 moles cyclohexane vapor at about 165 C. and 210 molesoxidizing gas per-hour were-introduced into the fourth reactor per hour.j

A vapo-r mixture of about 620 moles cyclohexane, 189 moles nitrogen, and25 moles water were removed per hour from the fourth reactor. A Vliquidproduct mixture of 1330 moles cyclohexane and 100 moles oxidized productwere recovered per hour.

The vapor streams from the reactor were condensedr and cyclohexanerecovered and recycled after separation of water contained therein.

The product mixture was hydrolyzed as describedin Example I and theorganic phase distilled to separate cyclohexane Which was recycled tothe reaction.

The product fraction was about'88% cyclohexanol and .cyclohexanone at acyclohexane conversion of 7%. The` EXAMPLE XVI For comparison purposes arun was made oxidizing cyclohexane with air with 6.2% by VWeightortho-boric acid and controlling the water partial pressure in excess ofabout 100 p.s.i.a. The temperature was 165 170 pressure results in poorselectivitiesof the order of those obtained with boron compoundaddition.

By selectivity in the foregoing is meant the molar percentage of reactedhydrocarbon which forms the alcohol or ketone. By conversion is meantthe percentage of hydrocarbon changed which is reacted.

t What is claimed is: L The process for the oxidationof a C4 to C3,saturated hydrocarbon to produce a borate ester containing oxidationreaction mixture wherein a molecular oxygen containing ga's is contactedin a reaction zone with a mixture of said hydrocarbon in the liquidphase and a lower hydrate of boric acid, comprising the combination ofeffecting said contact at a reaction temperature in the reaction zone inthe range of 140 to 180 C., removing a gaseous mixture comprising vaporsof said hydrocarbons and water from said liquid phase during theoxidation, and maintainingthepartial pressure of water in p.s.i. in saidgaseous mixture not greater than P Where P is given by the equation:

logm P=-1.85}0.0175(T) with T being the reaction temperature in degreesC., and

f tion reaction mixture wherein a molecular oxygen containing gasfiscontacted in a reaction zone with a mixture of said hydrocarbon in theliquid phase and meta boric acid,.comprising the combination ofeffecting said contact at a reaction temperature in the reaction zone inthe 'range of 140 to 180 C., removing a gaseous mixture comprisingvapors of said hydrocarbon and water from said liquidvphase during theoxidation, and maintaining the partial pressure of water in p.s.i. insaid gaseous mix- Vture leaving t-he said liquid phase in the range 2%to 100% of P where P is given vby the equation: f mgm P=1.85+o.0175(:r)

with T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

, 3. The process of claim 2 wherein said hydrocarbon is cyclohexane. t

f 4. Th-e process of claim 2 wherein said hydrocarbon is n-hexane. Y

V5.V The process of claim 2 wherein said hydrocarbon is methylcyclohexane.

6. rThe process for the oxidation of a C4 to C7 saturated hydrocarbon toproduce a borate ester containing oxidation lreaction mixture wherein amolecular oxygen containing gas is contacted in a reaction zone with amixture of said hydrocarbon in the liquid phase, and meta boric acid,comprising the combination of eecting said contact at a reactionVtemperature in the reaction zone in the range of 140 to 180 C.,continuously during the oxidation removinga gaseous mixture from saidliquid phase cornprising vapors of said hydrocarbon and water,continuously providing heat to said reaction Zone in addition to theheat of reaction, and maintaining the partial pressure of and pressurewas 500l p.s.i.g. At 12.7% cyclohexane conversion, the selectivity tocyclohexanol plus cyclo-hexanone was only about 64%. Y

This comparison clearly demonstrates that operation outside the scope ofthe invention at high water partial water in p.s.i. in said gaseousmixture leaving the said liquidphase in the range 2% to 100% of Pwherein P is given by the equation:

With-T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

7. The process for the oxidation of cyclohexane wherein a molecularoxygen containing gas is contacted with a mixture of cyclohexane in theliquid phase and meta boric acidV to produce a boraite ester reactionmixture comprising .the combination [of |effec-ting said lcontact alt -areaction .ternperature |in fthe reaction zone in :the range of to 180 C.continuing the contact until y4% to 25% of the cyclohexane is reacted,continuously during said contact removing a gaseous mixture containingvapors of said cyclohexane and water from said liquid phase condensing'the thus removed cyclohexane and water, separating the condensedcyclohexane, vaporizing separated cyclohexane, returning the vaporizedcyclohexane into contact with the liquid mixture in the reaction Zone,and maintaining the partial pressure of water in p.s.i. in the gaseousmixture leaving the liquid phase in the range 2% to 100% of P wherein Pis given by the equation:

with T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

8. The process of claim 7 wherein 8% to 20% of the cyclohexane isreacted.

9. The process for the oxidation of a C4 to C8, saturated hydrocarbon toproduce a borate ester containing oxidation reaction mixture wherein amolecular oxygen containing gas is contacted in a reaction zone with amixture of said hydrocarbon in the liquid phase and a lower hydrate ofboric acid, comprising the combination of effecting said contact at areaction temperature in the reaction zone in the range of 140 to 180 C.,removing a gaseous mixture comprising vapors of said hydrocarbons andwater from said liquid phase during the oxidation, and maintaining thepartial pressure of water in p.s.i. in said gaseous mixture not greaterthan P where P is given by the equation:A

logm P=0.01l12T-0.259

with T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

10. The process for the oxidation of a C4 to C8, saturated hydrocarbonto produce a borate ester containing oxidation reaction mixture whereina molecular oxygen containing gas is contacted in a reaction zone With amixture of said hydrocarbon in the liquid phase and meta boric acid,comprising the combination of affecting said contact ata reactiontemperature in the reaction zone in the range of 140 to 180 C., removinga gaseous mixture comprising vapors of said Ihydrocarbon and water fromsaid liquid phase during the oxidation, and maintaining the partialpressure of water in p.s.i. in said gaseous mixture leaving the saidliquid phase not greater than P where P is given by the equation:

logw P=0.0l112T-0.259

with T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

11. The process for the oxidation of a C4 to C7 saturated hydrocarbon toproduce a borate ester containing oxidation reaction mixture wherein amolecular oxygen containing gas is contacted in a reaction zone with amixture of said hydrocarbon in the liquid phase, and meta boric acid,comprising the combination of etlecting said contact at a reactiontemperature in the range of to C., continuously during the oxidationremoving a gaseous mixture from said liquid phase comprising vapors ofsaid hydrocarbon and water, continuously providing heat to said reactionzone in addition to the heat of reaction, and maintaining the partialpressure of Water in p.s.i. in said gaseous mixture leaving the saidliquid phase not greater than P where P is given by the equation:

with T being the reaction temperature in degrees C. and recovering theresulting oxidation reaction mixture.

12. The process for the oxidation of cyclohexane wherein a molecularoxygen containing gas is contacted with a mixture of cyclohexane in theliquid phase and meta boric acid to produce a borate ester reactionmixture comprising the combination `of effecting said contact at areaction temperature in the reaction zone in the range of 140 to 180 C.continuing the contact until 4% to 25% of the cyclohexane is reacted,continuously during said contact removing a gaseous mixture containingvapors of said cyclohexane and Water from said liquid phase condensingthe thus removed cyclohexane and Water, separating the condensedcyclohexane, vaporizing separated cyclohexane, returning the vaporizedcyclohexane into contact with the liquid mixture in the reaction zone,and maintaining the partial pressure of water p.s.i. in the gaseousmixture leaving the liquid phase not greater than P where P is given bythe equation:

logm P=o.01112T-0.259

with T being the reaction temperature in degrees C., and recovering theresulting oxidation reaction mixture.

No references cited.

CHARLES B. PARKER, Primary Examiner.

DELBERT R. PHILLIPS, Assistant Examiner.

1. THE PROCESS FOR THE OXIDATION OF A C4 TO C8, SATURATED HYDROCARBON TOPROUDUCE A BORATE ESTER CONTAINING OXIDATION REACTION MIXTURE WHEREIN AMOLECULAR OXYGEN CONTAINING GAS IS CONTACTED IN A REACTION ZONE WITH AMIXTURE OF SAID HYDROCARBON IN THE LIQUID PHASE AND A LOWER HYDRATE OFBORIC ACID, COMPRISING HE COMBINATION OF EFFECTING SAID CONTACT AT AREACTION TEMPERATURE IN THE REACTION ZONE IN THE RANGE OF 140* TO180*C., REMOVING A GASEOUS MIXTURE COMPRISING VAPORS OF SAIDHYDROCARBONS AND WATER FROM SAID LIQUID PHASE DURING THE OXIDATION, ANDMAINTAINING THE PARTIAL PRESSURE OF WATER IN P.S.I. IN SAID GASEOUSMIXTURE NOT GREATER THAN P WHERE P IS GIVEN BYTHE EQUATION: